Neural bases of autobiographical support for episodic recollection of faces

Differential effects of bilateral hippocampal CA3 damage on the implicit learning and recognition of complex event sequences

Learning regularities in the environment is a fundament of human cognition, which is supported by a network of brain regions that include the hippocampus. In two experiments, we assessed the effects of selective bilateral damage to human hippocampal subregion CA3, which was associated with autobiographical episodic amnesia extending ~50 years prior to the damage, on the ability to recognize complex, deterministic event sequences presented either in a spatial or a non-spatial configuration. In contrast to findings from related paradigms, modalities, and homologue species, hippocampal damage did not preclude recognition memory for an event sequence studied and tested at four spatial locations, whereas recognition memory for an event sequence presented at a single location was at chance. In two additional experiments, recognition memory for novel single-items was intact, whereas the ability to recognize novel single-items in a different location from that presented at study was at chance. The results are at variance with a general role of the hippocampus in the learning and recognition of complex event sequences based on non-adjacent spatial and temporal dependencies. We discuss the impact of the results on established theoretical accounts of the hippocampal contributions to implicit sequence learning and episodic memory.

A dynamic attractor network model of memory formation, reinforcement and forgetting

Empirical evidence shows that memories that are frequently revisited are easy to recall, and that familiar items involve larger hippocampal representations than less familiar ones. In line with these observations, here we develop a modelling approach to provide a mechanistic understanding of how hippocampal neural assemblies evolve differently, depending on the frequency of presentation of the stimuli. For this, we added an online Hebbian learning rule, background firing activity, neural adaptation and heterosynaptic plasticity to a rate attractor network model, thus creating dynamic memory representations that can persist, increase or fade according to the frequency of presentation of the corresponding memory patterns. Specifically, we show that a dynamic interplay between Hebbian learning and background firing activity can explain the relationship between the memory assembly sizes and their frequency of stimulation. Frequently stimulated assemblies increase their size independently from each other (i.e. creating orthogonal representations that do not share neurons, thus avoiding interference). Importantly, connections between neurons of assemblies that are not further stimulated become labile so that these neurons can be recruited by other assemblies, providing a neuronal mechanism of forgetting.

The neurobiology of vocal communication in marmosets

An increasingly popular animal model for studying the neural basis of social behavior, cognition, and communication is the common marmoset (Callithrix jacchus). Interest in this New World primate across neuroscience is now being driven by their proclivity for prosociality across their repertoire, high volubility, and rapid development, as well as their amenability to naturalistic testing paradigms and freely moving neural recording and imaging technologies. The complement of these characteristics set marmosets up to be a powerful model of the primate social brain in the years to come. Here, we focus on vocal communication because it is the area that has both made the most progress and illustrates the prodigious potential of this species. We review the current state of the field with a focus on the various brain areas and networks involved in vocal perception and production, comparing the findings from marmosets to other animals, including humans.

The Enigmatic CA2: Exploring the Understudied Region of the Hippocampus and Its Involvement in Parkinson's Disease

Parkinson's disease (PD) is a neurodegenerative disease that affects both motor and non-motor functions. Although motor impairment is a prominent clinical sign of PD, additional neurological symptoms may also occur, particularly in the preclinical and prodromal stages. Among these symptoms, social cognitive impairment is common and detrimental. This article aims to review non-motor symptoms in PD patients, focusing on social cognitive deficits. It also examines the specific characteristics of the CA2 region and its involvement in social behavior, highlighting recent advances and perspectives. Additionally, this review provides critical insights into and analysis of research conducted in rodents and humans, which may help improve the understanding of the current status of putative therapeutic strategies for social cognitive dysfunction in PD and potential avenues related to the function of the hippocampal CA2 region.

Recollection and prior knowledge recruit the left angular gyrus during recognition

The human angular gyrus (AG) is implicated in recollection, or the ability to retrieve detailed memory content from a specific episode. A separate line of research examining the neural bases of more general mnemonic representations, extracted over multiple episodes, also highlights the AG as a core region of interest. To reconcile these separate views of AG function, the present fMRI experiment used a Remember-Know paradigm with famous (prior knowledge) and non-famous (no prior knowledge) faces to test whether AG activity could be modulated by both task-specific recollection and general prior knowledge within the same individuals. Increased BOLD activity in the left AG was observed during both recollection in the absence of prior knowledge (recollected > non-recollected or correctly rejected non-famous faces) and when prior knowledge was accessed in the absence of experiment-specific recollection (famous > non-famous correct rejections). This pattern was most prominent for the left AG as compared to the broader inferior parietal lobe. Recollection-related responses in the left AG increased with encoding duration and prior knowledge, despite prior knowledge being incidental to the recognition decision. Overall, the left AG appears sensitive to both task-specific recollection and the incidental access of general prior knowledge, thus broadening our notions of the kinds of mnemonic representations that drive activity in this region.

Hippocampal contributions to social and cognitive deficits in autism spectrum disorder

Autism spectrum disorder (ASD) is characterized by hallmark impairments in social functioning. Nevertheless, nonsocial cognition, including hippocampus-dependent spatial reasoning and episodic memory, is also commonly impaired in ASD. ASD symptoms typically emerge between 12 and 24 months of age, a time window associated with critical developmental events in the hippocampus. Despite this temporal overlap and evidence of hippocampal structural abnormalities in ASD individuals, relatively few human studies have focused on hippocampal function in ASD. Herein, we review the existing evidence for the involvement of the hippocampus in ASD and highlight the hippocampus as a promising area of interest for future research in ASD.

Cholinergic transmission from the basal forebrain modulates social memory in male mice

Disruptions in social behaviour are prevalent in many neuropsychiatric disorders such as schizophrenia, bipolar disorder and autism spectrum disorders. However, the underlying neurochemical regulation of social behaviour is still not well understood. The central cholinergic system has been proposed to contribute to the regulation of social behaviour. For instance, decreased global levels of acetylcholine release in the brain leads to decreased social interaction and an impairment of social memory in mice. Nonetheless, it has been difficult to ascertain the specific brain areas where cholinergic signalling influences social preference and social memory. In this study, we investigated the impact of different forebrain cholinergic regions on social behaviour by examining mouse lines that differ in their regional expression level of the vesicular acetylcholine transporter-the protein that regulates acetylcholine secretion. We found that when cholinergic signalling is highly disrupted in the striatum, hippocampus, cortex and amygdala mice have intact social preference but are impaired in social memory, as they cannot remember a familiar conspecific nor recognize a novel one. A similar pattern emerges when acetylcholine release is disrupted mainly in the striatum, cortex, and amygdala; however, the ability to recognize novel conspecifics is retained. In contrast, cholinergic signalling of the striatum and amygdala does not appear to significantly contribute to the modulation of social memory and social preference. Furthermore, we demonstrated that increasing global cholinergic tone does not increase social behaviours. Together, these data suggest that cholinergic transmission from the hippocampus and cortex are important for regulating social memory.

Activation of Person Knowledge in Medial Prefrontal Cortex during the Encoding of New Lifelike Events

Our knowledge about people can help us predict how they will behave in particular situations and interpret their actions. In this study, we investigated the cognitive and neural effects of person knowledge on the encoding and retrieval of novel life-like events. Healthy human participants learnt about two characters over a week by watching 6 episodes of one of two situation comedies, which were both centered on a young couple. In the scanner, they watched and then silently recalled 20 new scenes from both shows that were all set in unfamiliar locations: 10 from their trained show and 10 from the untrained show. After scanning, participants' recognition memory was better for scenes from the trained show. The functional magnetic resonance imaging (fMRI) patterns of brain activity when watching the videos were reinstated during recall, but this effect was not modulated by training. However, person knowledge boosted the similarity in fMRI patterns of activity in the medial prefrontal cortex (MPFC) when watching the new events involving familiar characters. Our findings identify a role for the MPFC in the representation of schematic person knowledge during the encoding of novel, lifelike events.

Short timescale modulation of cortical and cerebellar activity in the early phase of motor sequence learning: an fMRI study

Motor learning is a multi-stage process, in which the involvement of different brain regions is related to the specific stage. We aimed at characterising short timescale changes of brain activity induced by motor sequence learning. Twenty healthy volunteers performed a serial reaction time task during an MRI session in a 3 T scanner. The task consisted of two conditions: repeated and random, that were compared over the whole fMRI run, as well as within sections, to investigate brain activity modulating related to the learning stage. The whole fMRI run analysis showed a stronger response for the repeated condition in fronto-parietal regions, cerebellum and thalamus. The analysis on sections showed initially increased right cerebellar activity. In the subsequent phase, bilateral cerebellar activity was observed, while no increased activity was seen in the last phase, when the learning was established. At the neocortical level, the repeated condition showed stronger activity at first in fronto-parietal regions bilaterally, then lateralized to the right hemisphere in the last learning phase. This study showed short time scale brain activity modulation in cortical and cerebellar regions with involvement of different brain regions over the learning process not restricted to the motor circuit.

The Influence of Prior Knowledge on Memory and Metamemory for Famous Names and Faces

Abstract. Two experiments examined the effect of prior knowledge on memory and metamemory for names and faces using famous 1960s and 2000s actors as the manipulation of prior knowledge. In Experiment 1, 66 participants studied the names of famous actors, half presented with their faces, with instructions to remember only the names. In Experiment 2, 56 participants studied the faces of these actors, half presented with their names, with instructions to remember only the faces. In both experiments, participants made immediate Judgments of Learning (JOLs) for each to-be-remembered stimulus followed by a test of recognition that used a Recollect/Familiar/No-Memory judgment. We found higher JOLs, recognition memory, and JOL accuracy for 2000s actors. Adding a name to a face or a face to a name increased JOLs while paradoxically decreasing memory. Back-sorting and binning analyses converged on the conclusion that immediate JOLs predicted memories accompanied by recollection but not familiarity.

Social spatial cognition: social distance dynamics as an identifier of social interactions

We suggest that socio-spatial behavior, which is an interaction between social and spatial cognition, can be viewed as a set of excursions that originate and end in close proximity to another individual(s). We present an extension of earlier studies that perceived spatial behavior in individual animals as a series of excursions originating from a particular location. We measured here the momentary distance between two individuals (social distance) to differentiate among eight possible types of social excursion originating in a state of proximity between excursion-participants. The defined excursion types are based on whether or not the excursion initiator also concludes the excursion, whether or not the excursion starts and ends at the same location, and the dynamics of the distance between excursion participants. We validated this approach to socio-spatial behavior as a set of excursions using it to analyze the behavior of the two sexes in rodents, of normal vs. stereotyped rats, as well as of different rodent species. Each of these groups displays a prevalent excursion type that reflects a distinct social dynamics. Our approach offers a useful and comprehensive tool for studying socio-spatial cognition, and can also be applied to distinguish among different social situations in rodents and other animals.

Altered structure and functional connectivity of the hippocampus are associated with social and mathematical difficulties in nonverbal learning disability

The hippocampus is known to play a critical role in a variety of complex abilities, including visual-spatial reasoning, social functioning, and math. Nonverbal learning disability (NVLD) is a neurodevelopmental disorder characterized by deficits in visual-spatial reasoning that are accompanied by impairment in social function or mathematics, as well as motor or executive function skills. Despite the overlap between behaviors supported by the hippocampus and impairments in NVLD, the structure and function of the hippocampus in NVLD has not been studied. To address this gap in the literature, we first compared hippocampal volume and resting-state functional connectivity in children with NVLD (n = 24) and typically developing (TD) children (n = 20). We then explored associations between hippocampal structure, connectivity, and performance on measures of spatial, social, and mathematical ability. Relative to TD children, those with NVLD showed significant reductions in left hippocampal volume and greater hippocampal-cerebellar connectivity. In children with NVLD, reduced hippocampal volume associated with worse mathematical problem solving. Although children with NVLD exhibited more social problems (social responsiveness scale [SRS]) and higher hippocampal-cerebellar connectivity relative to TD children, greater connectivity was associated with fewer social problems among children with NVLD but not TD children. Such an effect may suggest a compensatory mechanism. These structural and functional alterations of the hippocampus may disrupt its putative role in organizing conceptual frameworks through cognitive mapping, thus contributing to the cross-domain difficulties that characterize NVLD.

Inter-Network High-Order Functional Connectivity (IN-HOFC) and its Alteration in Patients with Mild Cognitive Impairment

Little is known about the high-order interactions among brain regions measured by the similarity of higher-order features (other than the raw blood-oxygen-level-dependent signals) which can characterize higher-level brain functional connectivity (FC). Previously, we proposed FC topographical profile-based high-order FC (HOFC) and found that this metric could provide supplementary information to traditional FC for early Alzheimer's disease (AD) detection. However, whether such findings apply to network-level brain functional integration is unknown. In this paper, we propose an extended HOFC method, termed inter-network high-order FC (IN-HOFC), as a useful complement to the traditional inter-network FC methods, for characterizing more complex organizations among the large-scale brain networks. In the IN-HOFC, both network definition and inter-network FC are defined in a high-order manner. To test whether IN-HOFC is more sensitive to cognition decline due to brain diseases than traditional inter-network FC, 77 mild cognitive impairments (MCIs) and 89 controls are compared among the conventional methods and our IN-HOFC. The result shows that IN-HOFCs among three temporal lobe-related high-order networks are dampened in MCIs. The impairment of IN-HOFC is especially found between the anterior and posterior medial temporal lobe and could be a potential MCI biomarker at the network level. The competing network-level low-order FC methods, however, either revealing less or failing to detect any group difference. This work demonstrates the biological meaning and potential diagnostic value of the IN-HOFC in clinical neuroscience studies.

Anterior retrosplenial cortex is required for long-term object recognition memory

The retrosplenial cortex (RSC) is implicated on navigation and contextual memory. Lesions studies showed that the RSC shares functional similarities with the hippocampus (HP). Here we evaluated the role of the anterior RSC (aRSC) in the “what” and “where” components of recognition memory and contrasted it with that of the dorsal HP (dHP). Our behavioral and molecular findings show functional differences between the aRSC and the dHP in recognition memory. The inactivation of the aRSC, but not the dHP, impairs the consolidation and expression of the “what” memory component. In addition, object recognition task is accompanied by c-Fos levels increase in the aRSC. Interestingly, we found that the aRSC is recruited to process the “what” memory component only if it is active during acquisition. In contrast, both the aRSC and dHP are required for encoding the “where” component, which correlates with c-Fos levels increase. Our findings introduce a novel role of the aRSC in recognition memory, processing not only the “where”, but also the “what” memory component.

A Computational Model of Visual Recognition Memory via Grid Cells

Models of face, object, and scene recognition traditionally focus on massively parallel processing of low-level features, with higher-order representations emerging at later processing stages. However, visual perception is tightly coupled to eye movements, which are necessarily sequential. Recently, neurons in entorhinal cortex have been reported with grid cell-like firing in response to eye movements, i.e., in visual space. Following the presumed role of grid cells in vector navigation, we propose a model of recognition memory for familiar faces, objects, and scenes, in which grid cells encode translation vectors between salient stimulus features. A sequence of saccadic eye-movement vectors, moving from one salient feature to the expected location of the next, potentially confirms an initial hypothesis (accumulating evidence toward a threshold) about stimulus identity, based on the relative feature layout (i.e., going beyond recognition of individual features). The model provides an explicit neural mechanism for the long-held view that directed saccades support hypothesis-driven, constructive perception and recognition; is compatible with holistic face processing; and constitutes the first quantitative proposal for a role of grid cells in visual recognition. The variance of grid cell activity along saccade trajectories exhibits 6-fold symmetry across 360 degrees akin to recently reported fMRI data. The model suggests that disconnecting grid cells from occipitotemporal inputs may yield prosopagnosia-like symptoms. The mechanism is robust with regard to partial visual occlusion, can accommodate size and position invariance, and suggests a functional explanation for medial temporal lobe involvement in visual memory for relational information and memory-guided attention.

The Hippocampus and Social Impairment in Psychiatric Disorders

Social deficits, such as poor social skills (i.e., the inability to engage in appropriate and effective social interactions) and social withdrawal, are prevalent across psychiatric disorders and often co-occur with hippocampal structural and functional abnormalities. The centrality of both social and hippocampal dysfunction in psychiatric research prompts the question: Are they linked? The social cognitive map framework provides a clue: The hippocampus tracks social information in the physical environment, maps others along social dimensions, and supports social memory and decision-making. Hippocampal dysfunction might disrupt social map representation and contribute to commonly seen social behavioral symptoms. This review summarizes evidence for the role of the hippocampus in social cognitive mapping, followed by evidence that hippocampal dysfunction and social dysfunction co-occur in psychiatric disorders. We argue that the co-occurrence of hippocampal and social impairment may be related via hippocampal social cognitive mapping.

Navigating Social Space

Cognitive maps are encoded in the hippocampal formation and related regions and range from the spatial to the purely conceptual. Neural mechanisms that encode information into relational structures, up to an arbitrary level of abstraction, may explain such a broad range of representation. Research now indicates that social life can also be mapped by these mechanisms: others' spatial locations, social memory, and even a two-dimensional social space framed by social power and affiliation. The systematic mapping of social life onto a relational social space facilitates adaptive social decision making, akin to social navigation. This emerging line of research has implications for cognitive mapping research, clinical disorders that feature hippocampal dysfunction, and the field of social cognitive neuroscience.

Practice effects in healthy older adults: Implications for treatment-induced neuroplasticity in Aphasia

In treating aphasic individuals with anomia, practice naming pictures leads to better performance as measured by accuracy and reaction time. The neurocognitive mechanisms supporting such improvements remain elusive, in part due to gaps in understanding the influence of practice on neurotypical older adults. The current study investigated the influence of practice naming one set of low frequency pictures of actions and objects in 18 healthy older adults, ten of whom were tested twice approximately one month apart. Both item and task practice effects were observed in improved accuracy and response latencies naming pictures in the scanner. This same facilitation effect was observed in neuroimaging results. For example, a significant main effect of practice was observed in bilateral precuneus and left inferior parietal lobule, characterized by greater activity for naming practiced vs. unpracticed pictures. This difference was significantly diminished in subsequent runs after exposure to unpracticed pictures. Whole brain analyses across two sessions showed that practice effects were specific to practice, i.e., there were not similar observable changes in contrasts examining actions vs. objects over time. These findings have important implications for understanding treatment-induced neuroplasticity in anomia treatment.

Effects of Prior-Knowledge on Brain Activation and Connectivity During Associative Memory Encoding

Forming new associations is a fundamental process of building our knowledge system. At the brain level, how prior-knowledge influences acquisition of novel associations has not been thoroughly investigated. Based on recent cognitive neuroscience literature on multiple-component memory processing, we hypothesize that prior-knowledge triggers additional evaluative, semantic, or episodic-binding processes, mainly supported by the ventromedial prefrontal cortex (vmPFC), anterior temporal pole (aTPL), and hippocampus (HPC), to facilitate new memory encoding. To test this hypothesis, we scanned 20 human participants with functional magnetic resonance imaging (fMRI) while they associated novel houses with famous or nonfamous faces. Behaviorally, we found beneficial effects of prior-knowledge on associative memory. At the brain level, we found that the vmPFC and HPC, as well as the parahippocampal place area (PPA) and fusiform face area, showed stronger activation when famous faces were involved. The vmPFC, aTPL, HPC, and PPA also exhibited stronger activation when famous faces elicited stronger emotions and memories, and when associations were later recollected. Connectivity analyses also suggested that HPC connectivity with the vmPFC plays a more important role in the famous than nonfamous condition. Taken together, our results suggest that prior-knowledge facilitates new associative encoding by recruiting additional perceptual, evaluative, or associative binding processes.

Ventromedial prefrontal cortex, adding value to autobiographical memories

The medial prefrontal cortex (mPFC) has been consistently implicated in autobiographical memory recall and decision making. Its function in decision making tasks is believed to relate to value representation, but its function in autobiographical memory recall is not yet clear. We hypothesised that the mPFC represents the subjective value of elements during autobiographical memory retrieval. Using functional magnetic resonance imaging during an autobiographical memory recall task, we found that the blood oxygen level dependent (BOLD) signal in ventromedial prefrontal cortex (vmPFC) was parametrically modulated by the affective values of items in participants’ memories when they were recalling and evaluating these items. An unrelated modulation by the participant’s familiarity with the items was also observed. During retrieval of the event, the BOLD signal in the same region was modulated by the personal significance and emotional intensity of the memory, which was correlated with the values of the items within them. These results support the idea that vmPFC processes self-relevant information, and suggest that it is involved in representing the personal emotional values of the elements comprising autobiographical memories.

Categorical perception of familiarity: Evidence for a hyper-familiarity in schizophrenia

Familiarity is a crucial aspect of recognition that may be perturbed in schizophrenia patients (SZP) and may lead to delusional disorders. However, there are no existing guidelines on how to assess and treat familiarity disorders in schizophrenia. Some experimental studies have investigated familiarity processing in SZP but have produced inconsistent results, which are likely a result of methodological issues. Moreover, these studies only assessed whether familiarity processing is preserved or impaired in SZP, but not the tendency of SZP to consider unfamiliar stimuli to be familiar. By using a familiarity continuum task based on the existence of the categorical perception effect, the objective of this study was to determine whether SZP present hyper- or hypo-familiarity. To this purpose, 15 SZP and 15 healthy subjects (HS) were presented with facial stimuli, which consisted of picture morphs of unfamiliar faces and faces that were personally familiar to the participants. The percentage of the familiar face contained in the morph ranged from 5 to 95%. The participants were asked to press a button when they felt familiar with the face that was presented. The main results revealed a higher percentage of familiarity responses for SZP compared with HS from the stimuli with low levels of familiarity in the morph and a lower familiarity threshold, suggesting a hyper-familiarity disorder in SZP. Moreover, the intensity of this "hyper-familiarity" was correlated with positive symptoms. This finding clearly suggests the need for a more systematic integration of an assessment of familiarity processing in schizophrenia symptoms assessments.

Neural microgenesis of personally familiar face recognition

Despite a wealth of information provided by neuroimaging research, the neural basis of familiar face recognition in humans remains largely unknown. Here, we isolated the discriminative neural responses to unfamiliar and familiar faces by slowly increasing visual information (i.e., high-spatial frequencies) to progressively reveal faces of unfamiliar or personally familiar individuals. Activation in ventral occipitotemporal face-preferential regions increased with visual information, independently of long-term face familiarity. In contrast, medial temporal lobe structures (perirhinal cortex, amygdala, hippocampus) and anterior inferior temporal cortex responded abruptly when sufficient information for familiar face recognition was accumulated. These observations suggest that following detailed analysis of individual faces in core posterior areas of the face-processing network, familiar face recognition emerges categorically in medial temporal and anterior regions of the extended cortical face network.

Long-term memory for odors: influences of familiarity and identification across 64 days

Few studies have investigated long-term odor recognition memory, although some early observations suggested that the forgetting rate of olfactory representations is slower than for other sensory modalities. This study investigated recognition memory across 64 days for high and low familiar odors and faces. Memory was assessed in 83 young participants at 4 occasions; immediate, 4, 16, and 64 days after encoding. The results indicated significant forgetting for odors and faces across the 64 days. The forgetting functions for the 2 modalities were not fundamentally different. Moreover, high familiar odors and faces were better remembered than low familiar ones, indicating an important role of semantic knowledge on recognition proficiency for both modalities. Although odor recognition was significantly better than chance at the 64 days testing, memory for the low familiar odors was relatively poor. Also, the results indicated that odor identification consistency across sessions, irrespective of accuracy, was positively related to successful recognition.

Familiarity and recollection in heuristic decision making

Heuristics involve the ability to utilize memory to make quick judgments by exploiting fundamental cognitive abilities. In the current study we investigated the memory processes that contribute to the recognition heuristic and the fluency heuristic, which are both presumed to capitalize on the byproducts of memory to make quick decisions. In Experiment 1, we used a city-size comparison task while recording event-related potentials (ERPs) to investigate the potential contributions of familiarity and recollection to the 2 heuristics. ERPs were markedly different for recognition heuristic-based decisions and fluency heuristic-based decisions, suggesting a role for familiarity in the recognition heuristic and recollection in the fluency heuristic. In Experiment 2, we coupled the same city-size comparison task with measures of subjective preexperimental memory for each stimulus in the task. Although previous literature suggests the fluency heuristic relies on recognition speed alone, our results suggest differential contributions of recognition speed and recollected knowledge to these decisions, whereas the recognition heuristic relies on familiarity. Based on these results, we created a new theoretical framework that explains decisions attributed to both heuristics based on the underlying memory associated with the choice options.

Stimulus familiarity modulates functional connectivity of the perirhinal cortex and anterior hippocampus during visual discrimination of faces and objects

Recent research suggests that the medial temporal lobe (MTL) is involved in perception as well as in declarative memory. Amnesic patients with focal MTL lesions and semantic dementia patients showed perceptual deficits when discriminating faces and objects. Interestingly, these two patient groups showed different profiles of impairment for familiar and unfamiliar stimuli. For MTL amnesics, the use of familiar relative to unfamiliar stimuli improved discrimination performance. By contrast, patients with semantic dementia—a neurodegenerative condition associated with anterolateral temporal lobe damage—showed no such facilitation from familiar stimuli. Given that the two patient groups had highly overlapping patterns of damage to the perirhinal cortex, hippocampus, and temporal pole, the neuroanatomical substrates underlying their performance discrepancy were unclear. Here, we addressed this question with a multivariate reanalysis of the data presented by Barense et al. (2011), using functional connectivity to examine how stimulus familiarity affected the broader networks with which the perirhinal cortex, hippocampus, and temporal poles interact. In this study, healthy participants were scanned while they performed an odd-one-out perceptual task involving familiar and novel faces or objects. Seed-based analyses revealed that functional connectivity of the right perirhinal cortex and right anterior hippocampus was modulated by the degree of stimulus familiarity. For familiar relative to unfamiliar faces and objects, both right perirhinal cortex and right anterior hippocampus showed enhanced functional correlations with anterior/lateral temporal cortex, temporal pole, and medial/lateral parietal cortex. These findings suggest that in order to benefit from stimulus familiarity, it is necessary to engage not only the perirhinal cortex and hippocampus, but also a network of regions known to represent semantic information.

Social cognition and the cerebellum: a meta-analysis of over 350 fMRI studies

This meta-analysis explores the role of the cerebellum in social cognition. Recent meta-analyses of neuroimaging studies since 2008 demonstrate that the cerebellum is only marginally involved in social cognition and emotionality, with a few meta-analyses pointing to an involvement of at most 54% of the individual studies. In this study, novel meta-analyses of over 350 fMRI studies, dividing up the domain of social cognition in homogeneous subdomains, confirmed this low involvement of the cerebellum in conditions that trigger the mirror network (e.g., when familiar movements of body parts are observed) and the mentalizing network (when no moving body parts or unfamiliar movements are present). There is, however, one set of mentalizing conditions that strongly involve the cerebellum in 50-100% of the individual studies. In particular, when the level of abstraction is high, such as when behaviors are described in terms of traits or permanent characteristics, in terms of groups rather than individuals, in terms of the past (episodic autobiographic memory) or the future rather than the present, or in terms of hypothetical events that may happen. An activation likelihood estimation (ALE) meta-analysis conducted in this study reveals that the cerebellum is critically implicated in social cognition and that the areas of the cerebellum which are consistently involved in social cognitive processes show extensive overlap with the areas involved in sensorimotor (during mirror and self-judgments tasks) as well as in executive functioning (across all tasks). We discuss the role of the cerebellum in social cognition in general and in higher abstraction mentalizing in particular. We also point out a number of methodological limitations of some available studies on the social brain that hamper the detection of cerebellar activity.

Distinguishable neurofunctional effects of task practice and item practice in picture naming: a BOLD fMRI study in healthy subjects

Practice of language tasks results in improved performance and BOLD signal changes. We distinguish changes correlated with repeated exposure to a picture naming task, from changes associated with naming specific items trained during practice. Task practice affected trained and untrained items, yielding left-sided BOLD deactivations in extrastriate, prefrontal and superior temporal areas (consistent with their putative role in perceptual priming, articulatory planning and phonological lexical retrieval, respectively). Item practice effects were restricted to trained words. There was deactivation in left posterior fusiform (supporting its role in accessing structural object representations), anterior cingulate and left insular/inferior frontal cortices (consistent with their role in processing low-frequency words). Central precuneus and posterior cingulate were hyperactivated (consistent with their putative role in episodic memory for trained items, probably due to functional connections with language areas). In healthy subjects, naming practice modifies stored linguistic representations, but mostly affects ease of access to trained words.

Action observers implicitly expect actors to act goal-coherently, even if they do not: an fMRI study

Actions observed in everyday life normally consist of one person performing sequences of goal-directed actions. The present fMRI study tested the hypotheses that observers are influenced by the actor's identity, even when this information is task-irrelevant, and that this information shapes their expectation on subsequent actions of the same actor. Participants watched short video clips of action steps that either pertained to a common action with an overarching goal or not, and were performed by either one or by varying actors (2 × 2 design). Independent of goal coherence, actor coherence elicited activation in dorsolateral and ventromedial frontal cortex, together pointing to a spontaneous attempt to integrate all actions performed by one actor. Interestingly, watching an actor performing unrelated actions elicited additional activation in left inferior frontal gyrus, suggesting a search in semantic memory in an attempt to construct an overarching goal that can reconcile the disparate action steps with a coherent intention. Post-experimental surveys indicate that these processes occur mostly unconsciously. Findings strongly suggest a spontaneous expectation bias toward actor-related episodes in action observers, and hence to the immense impact of actor information on action observation.

In search of the trauma memory: a meta-analysis of functional neuroimaging studies of symptom provocation in posttraumatic stress disorder (PTSD)

Notwithstanding some discrepancy between results from neuroimaging studies of symptom provocation in posttraumatic stress disorder (PTSD), there is broad agreement as to the neural circuit underlying this disorder. It is thought to be characterized by an exaggerated amygdalar and decreased medial prefrontal activation to which the elevated anxiety state and concomitant inadequate emotional regulation are attributed. However, the proposed circuit falls short of accounting for the main symptom, unique among anxiety disorders to PTSD, namely, reexperiencing the precipitating event in the form of recurrent, distressing images and recollections. Owing to the technical demands, neuroimaging studies are usually carried out with small sample sizes. A meta-analysis of their findings is more likely to cast light on the involved cortical areas. Coordinate-based meta-analyses employing ES-SDM (Effect Size Signed Differential Mapping) were carried out on 19 studies with 274 PTSD patients. Thirteen of the studies included 145 trauma-exposed control participants. Comparisons between reactions to trauma-related stimuli and a control condition and group comparison of reactions to the trauma-related stimuli were submitted to meta-analysis. Compared to controls and the neutral condition, PTSD patients showed significant activation of the mid-line retrosplenial cortex and precuneus in response to trauma-related stimuli. These midline areas have been implicated in self-referential processing and salient autobiographical memory. PTSD patients also evidenced hyperactivation of the pregenual/anterior cingulate gyrus and bilateral amygdala to trauma-relevant, compared to neutral, stimuli. Patients showed significantly less activation than controls in sensory association areas such as the bilateral temporal gyri and extrastriate area which may indicate that the patients' attention was diverted from the presented stimuli by being focused on the elicited trauma memory. Being involved in associative learning and priming, the retrosplenial cortex may have an important function in relation to trauma memory, in particular, the intrusive reexperiencing of the traumatic event.

Portraying the unique contribution of the default mode network to internally driven mnemonic processes

Numerous neuroimaging studies have implicated default mode network (DMN) involvement in both internally driven processes and memory. Nevertheless, it is unclear whether memory operations reflect a particular case of internally driven processing or alternatively involve the DMN in a distinct manner, possibly depending on memory type. This question is critical for refining neurocognitive memory theorem in the context of other endogenic processes and elucidating the functional significance of this key network. We used functional MRI to examine DMN activity and connectivity patterns while participants overtly generated words according to nonmnemonic (phonemic) or mnemonic (semantic or episodic) cues. Overall, mnemonic word fluency was found to elicit greater DMN activity and stronger within-network functional connectivity compared with nonmnemonic fluency. Furthermore, two levels of functional organization of memory retrieval were shown. First, across both mnemonic tasks, activity was greater mainly in the posterior cingulate cortex, implying selective contribution to generic aspects of memory beyond its general involvement in endogenous processes. Second, parts of the DMN showed distinct selectivity for each of the mnemonic conditions; greater recruitment of the anterior prefrontal cortex, retroesplenial cortex, and hippocampi and elevated connectivity between anterior and posterior medial DMN nodes characterized the semantic condition, whereas increased recruitment of posterior DMN components and elevated connectivity between them characterized the episodic condition. This finding emphasizes the involvement of DMN elements in discrete aspects of memory retrieval. Altogether, our results show a specific contribution of the DMN to memory processes, corresponding to the specific type of memory retrieval.

Anterior temporal face patches: a meta-analysis and empirical study

Evidence suggests the anterior temporal lobe (ATL) plays an important role in person identification and memory. In humans, neuroimaging studies of person memory report consistent activations in the ATL to famous and personally familiar faces and studies of patients report resection or damage of the ATL causes an associative prosopagnosia in which face perception is intact but face memory is compromised. In addition, high-resolution fMRI studies of non-human primates and electrophysiological studies of humans also suggest regions of the ventral ATL are sensitive to novel faces. The current study extends previous findings by investigating whether similar subregions in the dorsal, ventral, lateral, or polar aspects of the ATL are sensitive to personally familiar, famous, and novel faces. We present the results of two studies of person memory: a meta-analysis of existing fMRI studies and an empirical fMRI study using optimized imaging parameters. Both studies showed left-lateralized ATL activations to familiar individuals while novel faces activated the right ATL. Activations to famous faces were quite ventral, similar to what has been reported in previous high-resolution fMRI studies of non-human primates. These findings suggest that face memory-sensitive patches in the human ATL are in the ventral/polar ATL.

Social cognition and the anterior temporal lobes: a review and theoretical framework

Memory for people and their relationships, along with memory for social language and social behaviors, constitutes a specific type of semantic memory termed social knowledge. This review focuses on how and where social knowledge is represented in the brain. We propose that portions of the anterior temporal lobe (ATL) play a critical role in representing and retrieving social knowledge. This includes memory about people, their names and biographies and more abstract forms of social memory such as memory for traits and social concepts. This hypothesis is based on the convergence of several lines of research including anatomical findings, lesion evidence from both humans and non-human primates and neuroimaging evidence. Moreover, the ATL is closely interconnected with cortical nuclei of the amygdala and orbitofrontal cortex via the uncinate fasciculus. We propose that this pattern of connectivity underlies the function of the ATL in encoding and storing emotionally tagged knowledge that is used to guide orbitofrontal-based decision processes.

Factors affecting medial temporal lobe engagement for past and future episodic events: an ALE meta-analysis of neuroimaging studies

Remembering the past and envisioning the future are at the core of one's sense of identity. Neuroimaging studies investigating the neural substrates underlying past and future episodic events have been growing in number. However, the experimental paradigms used to select and elicit episodic events vary greatly, leading to disparate results, especially with respect to the laterality and antero-posterior localization of hippocampal and adjacent medial temporal activations (i.e., parahippocampal, entorhinal and perirhinal cortices, amygdala). Although a central concern in today's literature, the issue of hippocampal and medial temporal lobe laterality and antero-posterior segregation in past and future episodic events has not yet been addressed extensively. Using the activation likelihood estimation (ALE) procedure (Turkeltaub, Eden, Jones, & Zeffiro, 2002), we performed a meta-analysis of hippocampal and adjacent medial temporal coordinates extracted from neuroimaging studies examining past remembering and future envisioning. We questioned whether methodological choices could influence the laterality of activations, namely (1) the type of cue used (generic vs. specific), (2) the type of task performed (recognition vs. recall/imagine), (3) the nature of the information retrieved (episodic vs. "strictly" episodic events) and (4) the age of participants. We consider "strictly" episodic events as events which are not only spatio-temporally unique and personal like episodic events, but are also associated with contextual and phenomenological details. These four factors were compared two-by-two, generating eight whole-brain statistical maps. Results indicate that (1) specific cues tend to activate more the right anterior hippocampus compared to the use of generic cues, (2) recall/imagine tasks tend to recruit more the left posterior parahippocampal gyrus compared to recognition tasks, (3) (re/pre)experiencing strictly episodic events tends to activate more the bilateral posterior hippocampus compared to episodic events and (4) older subjects tend to activate more the right anterior hippocampus compared to younger subjects. Importantly, our results stress that strictly episodic events triggered by specific cues elicit greater left posterior hippocampal activation than episodic events triggered by specific cues. These findings suggest that such basic methodological choices have an impact on the conclusions reached regarding past and future (re/pre)experiencing and their neural substrates.

Differential neural activity in the recognition of old versus new events: an activation likelihood estimation meta-analysis

This study presents a meta-analysis comparing hit and correct rejection (CR) conditions across 48 fMRI studies. Old/new (hit > CR) effects associated most consistently with (1) components of the default-mode network, including the left angular gyrus, bilateral precuneus, and bilateral posterior cingulate regions, which may support the mental re-experiencing of an old event, or ecphory; (2) components of the cognitive-control network, involving the left dorsolateral and dorsomedial prefrontal cortex and bilateral intraparietal sulcus regions, which may mediate memory and non-memory control functions; and (3) the caudate nucleus, a key part of the brain's reward system that may support the satisfaction tied to target-detection. Direct comparisons of old/new effects between item versus source retrieval and "remember" versus "know" retrieval yielded three main sets of findings. First, default-mode network regions showed greater old/new effects in conditions associated with richer ecphoric processing. Second, cognitive-control network regions showed greater old/new effects in conditions associated with a greater demand for strategic-retrieval processing. Third, the caudate nucleus showed greater old/new effects in conditions tied to greater confidence in target-detection. New/old (CR > hit) effects most strongly associated with the bilateral medial temporal lobe, possibly reflecting greater encoding-related activity for new than for old items, and the right posterior middle temporal regions, possibly reflecting repetition-related neural priming for old items. In conclusion, neural activity distinguishing old from new events comprises an ensemble of multiple memory-specific activities, including encoding, retrieval, and priming, as well as multiple types of more general cognitive activities, including default-mode, cognitive-control, and reward processing.

Age-related reorganization of functional networks for successful conflict resolution: a combined functional and structural MRI study

Aging has readily observable effects on the ability to resolve conflict between competing stimulus attributes that are likely related to selective structural and functional brain changes. To identify age-related differences in neural circuits subserving conflict processing, we combined structural and functional MRI and a Stroop Match-to-Sample task involving perceptual cueing and repetition to modulate resources in healthy young and older adults. In our Stroop Match-to-Sample task, older adults handled conflict by activating a frontoparietal attention system more than young adults and engaged a visuomotor network more than young adults when processing repetitive conflict and when processing conflict following valid perceptual cueing. By contrast, young adults activated frontal regions more than older adults when processing conflict with perceptual cueing. These differential activation patterns were not correlated with regional gray matter volume despite smaller volumes in older than young adults. Given comparable performance in speed and accuracy of responding between both groups, these data suggest that successful aging is associated with functional reorganization of neural systems to accommodate functionally increasing task demands on perceptual and attentional operations.

Perception and conception: temporal lobe activity during complex discriminations of familiar and novel faces and objects

Recent studies indicate that medial-temporal lobe (MTL) damage, either from focal lesions or neurodegenerative disease (e.g., semantic dementia), impairs perception as well as long-term declarative memory. Notably, however, these two patient groups show different performance for meaningful versus unfamiliar stimuli. In amnesics with nonprogressive MTL lesions, the use of meaningful stimuli, compared with unfamiliar items, boosted discrimination performance. In semantic dementia, a condition characterized by progressive deterioration of conceptual knowledge in the context of anterolateral temporal lobe damage, performance for meaningful stimuli was equivalent to that for unfamiliar items. To further investigate these findings, we scanned healthy volunteers while they performed odd-one-out discriminations involving familiar (i.e., meaningful/famous) and unfamiliar (i.e., novel) objects and faces and a baseline task of size oddity. Outside the scanner, volunteers' recognition memory was assessed. We found above baseline activity in the perirhinal cortex and hippocampus for all object and face discriminations and above baseline activity in the temporal pole for all face discriminations. The comparison of meaningful, relative to novel, faces and objects, revealed increased activity in the perirhinal cortex and hippocampus. In the temporal pole, we also found activity related to meaningfulness for faces but not for objects. Importantly, these meaningfulness effects were evident even for discriminations that were not subsequently well remembered, suggesting that the difference between meaningful and novel stimuli reflects perceptual or conceptual processes rather than solely incidental encoding into long-term memory. The results provide further evidence that the MTL is recruited during complex perceptual discrimination and additionally suggest that these structures are recruited in semantic processing of objects and faces.

Do we mind other minds when we mind other minds' actions? A functional magnetic resonance imaging study

Action observation engages higher motor areas, possibly reflecting an internal simulation. However, actions considered odd or unusual were found to trigger additional activity in the so-called theory of mind (ToM) network, pointing to deliberations on the actor's mental states. In this functional magnetic resonance imaging study, the hypothesis was tested that an allocentric perspective on a normal action, and even more so the sight of the actor's face, suffices to evoke ToM activity. Subjects observed short videos of object manipulation filmed from either the egocentric or the allocentric perspective, the latter including the actor's face in half of the trials. On the basis of a regions of interest analysis using ToM coordinates, we found increased neural activity in several regions of the ToM network. First, perceiving actions from an allocentric compared with the egocentric perspective enhanced activity in the left temporoparietal junction (TPJ). Second, the presence of the actor's face enhanced activation in the TPJ bilaterally, the medial prefrontal cortex (mPFC) and posterior cingulate cortex (PCC). Finally, the mPFC and PCC showed increased responses when the actor changed with respect to the preceding trial. These findings were further corroborated by zmap findings for the latter two contrasts. Together, findings indicate that observation of normal everyday actions can engage ToM areas and that an allocentric perspective, seeing the actor's face and seeing a face switch, are effective triggers.

Memory formation and long-term retention in humans and animals: convergence towards a transformation account of hippocampal-neocortical interactions

Historically, the hippocampus has been viewed as a temporary memory structure. Consistent with the central premise of standard consolidation theory (SCT), a memory is initially hippocampus-dependent but, over time, it undergoes a consolidation process and eventually becoming represented in a distributed cortical network independent of the hippocampus. In this paper, we review evidence that is incompatible with each of the following essential features of SCT that are derived from its central premise: (1) Hippocampal damage reliably produces temporally graded retrograde amnesia, (2) all declarative explicit memories are equivalent with respect to consolidation, (3) consolidation entails a process of duplication in which a particular cortically based memory is identical to the hippocampus-dependent memory from which it derived, (4) consolidated memories are permanent and immutable. We propose an alternative hypothesis that assumes a transformation process and changes in the memory over time. Building on multiple trace theory (Nadel & Moscovitch, 1997), the transformation hypothesis contains three key elements that differentiate it from SCT: (1) An initially formed memory, which is assumed to be episodic and context-bound, remains dependent on the hippocampus for as long as it is available, (2) with time and experience, a hippocampal memory supports the development, in neocortex, of a less integrated, schematic version, which retains the gist of the original memory, but few of its contextual details, (3) there is a dynamic interplay between the two types of memory such that one or another may be dominant, depending on the circumstances at retrieval. Evidence is provided in support of the transformation hypothesis, which is advanced as a framework for unifying the seemingly disparate results of studies of anterograde and retrograde memory in the animal and human literatures.

Beyond the memory mechanism: person-selective and nonselective processes in recognition of personally familiar faces

Special processes recruited during the recognition of personally familiar people have been assumed to reflect the rich episodic and semantic information that selectively represents each person. However, the processes may also include person nonselective ones, which may require interpretation in terms beyond the memory mechanism. To examine this possibility, we assessed decrease in differential activation during the second presentation of an identical face (repetition suppression) as an index of person selectivity. During fMRI, pictures of personally familiar, famous, and unfamiliar faces were presented to healthy subjects who performed a familiarity judgment. Each face was presented once in the first half of the experiment and again in the second half. The right inferior temporal and left inferior frontal gyri were activated during the recognition of both types of familiar faces initially, and this activation was suppressed with repetition. Among preferentially activated regions for personally familiar over famous faces, robust suppression in differential activation was exhibited in the bilateral medial and anterior temporal structures, left amygdala, and right posterior STS, all of which are known to process episodic and semantic information. On the other hand, suppression was minimal in the posterior cingulate, medial prefrontal, right inferior frontal, and intraparietal regions, some of which were implicated in social cognition and cognitive control. Thus, the recognition of personally familiar people is characterized not only by person-selective representation but also by nonselective processes requiring a research framework beyond the memory mechanism, such as a social adaptive response.

How reliable are visual context effects in the parahippocampal place area?

The parahippocampal place area (PPA) is a region of human cortex that responds more strongly to visual scenes (e.g., landscapes or cityscapes) than to other visual stimuli. It has been proposed that the primary function of the PPA is encoding of contextual information about object co-occurrence. Supporting this context hypothesis are reports that the PPA responds more strongly to strong-context than to weak-context objects and more strongly to famous faces (for which contextual associations are available) than to nonfamous faces. We reexamined the reliability of these 2 effects by scanning subjects with functional magnetic resonance imaging while they viewed strong- and weak-context objects, scrambled versions of these objects, and famous and nonfamous faces. "Contextual" effects for objects were observed to be reliable in the PPA at slow presentation rates but not at faster presentation rates intended to discourage scene imagery. We were unable to replicate the earlier finding of preferential PPA response to famous versus nonfamous faces. These results are difficult to reconcile with the hypothesis that the PPA encodes contextual associations but are consistent with a competing hypothesis that the PPA encodes scenic layout.

The effect of Neuregulin 1 on neural correlates of episodic memory encoding and retrieval

Neuregulin 1 (NRG1) has been found to be associated with schizophrenia. Impaired performance in episodic memory tasks is an often replicated finding in this disorder. In functional neuroimaging studies, this dysfunction has been linked to signal changes in prefrontal and medial temporal areas. Therefore, it is of interest whether genes associated with the disorder, such as NRG1, modulate episodic memory performance and its neural correlates. Ninety-four healthy individuals performed an episodic memory encoding and a retrieval task while brain activation was measured with functional MRI. All subjects were genotyped for the single nucleotide polymorphism (SNP) rs35753505 in the NRG1 gene. The effect of genotype on brain activation was assessed with fMRI during the two tasks. While there were no differences in performance, brain activation in the cingulate gyrus (BA 24), the left middle frontal gyrus (BA 9), the bilateral fusiform gyrus and the left middle occipital gyrus (BA 19) was positively correlated with the number of risk alleles in NRG1 during encoding. During retrieval brain activation was positively correlated with the number of risk alleles in the left middle occipital gyrus (BA 19). NRG1 genotype does modulate brain activation during episodic memory processing in key areas for memory encoding and retrieval. The results suggest that subjects with risk alleles show hyperactivations in areas associated with elaborate encoding strategies.

Human medial temporal lobe neurons respond preferentially to personally relevant images

People with whom one is personally acquainted tend to elicit richer and more vivid memories than people with whom one does not have a personal connection. Recent findings from neurons in the human medial temporal lobe (MTL) have shown that individual cells respond selectively and invariantly to representations of famous people [Quian Quiroga R, Reddy L, Kreiman G, Koch C, Fried I (2005) Nature 435(7045):1102-1107]. Observing these cells, we wondered whether photographs of personally relevant individuals, such as family members, might be more likely to generate such responses. To address this issue, we recorded the activity of 2,330 neurons in the human MTL while patients viewed photographs of varying personal relevance: previously unknown faces and landscapes, familiar but not necessarily personally relevant faces and landscapes, and finally, photographs of the patients themselves, their families, and the experimenters. Our findings indicate that personally relevant photographs are indeed more likely to elicit selective responses in MTL neurons than photographs of individuals with whom the patients have had no personal contact. These findings further suggest that relevant stimuli are encoded by a larger proportion of neurons than less relevant stimuli, given that familiar or personally relevant items are linked to a larger variety of experiences and memories of these experiences.

The hippocampus supports recognition memory for familiar words but not unfamiliar faces

Bilateral damage to the human hippocampus profoundly impairs the ability to form long-term, consciously accessible memories, producing a classic amnesic syndrome. However, the effect of hippocampal damage on our ability to recognize items via a feeling of familiarity is hotly disputed. Dual-process theory predicts no effect, whereas declarative memory theory predicts impairment of all types of recognition memory. Here, we demonstrate a striking material specificity in the effect of focal hippocampal damage: Recognition memory is impaired for words but intact for faces. The latter finding is incompatible with declarative memory theory, whereas the former constrains dual-process theory by revealing the limitations of postulated extrahippocampal familiarity-based processes. We suggest that the hippocampus boosts recognition of well-known stimuli (high-frequency words) by activating pre-experimental associations that enrich the context of their presentation. By contrast, recognition memory for some kinds of previously unfamiliar stimuli (unfamiliar faces) may be supported by extrahippocampal familiarity-based processes, at least over short intervals.